Heat shock protein 70 (Hsp70) is widely present in nucleus, cytoplasm, endoplasmic reticulum, mitochondria and chloroplast cells, and is involved in intracellular protein de novo synthesis, orientation, protein maturation and degradation of misfolded proteins, thus affecting the growth and metabolism function of cells. In cells, Hsp70 binding tonascent polypeptides on ribosome can prevent misfolding of nascent polypeptides; Hsp70 is essential for remodeling clathrin in the process of pinocytosis of mammalian cells; and Hsp70 binding to non native conformation proteins can promote proper folding and assembly of proteins, and can maintain extended conformation of protein precursors and prevent their aggregation denaturation and degradation, allowing easy transport to organelles.
Studies have shown that, Hsp70 is related to many diseases, such as tumors, neurodegenerative diseases, allograft rejection or infection and the like. In cancer cells, Hsp70 affects apoptosis mainly through the following pathways: (1) mitochondrial pathway: in the early stage of mitochondria, Hsp70 blocks migration of Bax, and decreases permeability of mitochondrial outer membrane, thereby inhibiting the release of cytc and AIF from mitochondria; in the late stage of mitochondria, Hsp70 binds directly to Apaf1, blocks the aggregation of procaspase-9, so that apoptotic body cannot be formed, and caspase-3 downstream cannot be activated; (2) death receptor pathway: Hsp70, by inhibiting the activation of JNK, and binding to Akt and PKC, triggers dephosphorylation of kinase, and allows protein stabilization, cell survival; similarly, Hsp70 can also bind to DR4 and DR5, and inhibit TRAIL-induced DISC aggregation and activity; (3) DNA degradation pathway: the complex of Hsp70, Hsp40, ICAD can inhibit the activity and folding effect of DNase CAD, prevent late apoptotic chromosomal DNA from being degraded, so as to achieve anti-apoptosis effect.
Study on Hsp70 useful for tumor therapy has become a hot spot in recent years, but a highly active inhibitor has not found yet, and the mechanism of action is not clear. In tumor cells, Hsp70 and its related protein expression are abnormally high. Experiments prove that after dosing stimulation tumor cells play a potential defense mechanism via protein Hsp70 to produce drug resistance, causing a decrease in activity of the drug. Hsp70 inhibitor is expected to reverse the antitumor drug resistance of tumor cell lines.